1. Field of the Invention
The present invention relates to an opto-electrical patterned substrate and a manufacturing method thereof, and more particularly to a substrate having a first patterned structure of micron-scale and a second patterned structure of submicron-scale, and to a light-emitting diode having the same.
2. Description of Related Art
The development of human's lighting history has come to an era of solid-state lighting, and what is the common goal pursued in the industry of solid-state lighting is to provide a higher light-emitting brightness, cheaper price, longer life, and higher stability, and so on. The most important demand in the lighting market is the brightness of the light-emitting diode. In general, the maximum light output (Lmax) of a light-emitting diode is mainly determined by the external quantum efficiency (ηext) and the maximum operating current (Imax), i.e. Lmax=ηext×Imax, wherein the external quantum efficiency (ηext) is determined by the internal quantum efficiency (ηint) and light extraction efficiency (ηext), i.e. ηext=ηint×ηextr. Currently, a typical blue light emitting diode has an internal quantum efficiency of 70% or more, but a green light emitting diode has a suddenly dropped internal quantum efficiency of 40% or less. Therefore, there is still a large growing space for improvement in the external quantum efficiency of light emitting diode or the light-emitting brightness of light emitting diode by elevating the internal quantum efficiency and the light extraction efficiency.
The lattice mismatch between GaN and a sapphire substrate is as high as 16%. Therefore, when the sapphire substrate is used as a substrate for GaN epitaxy, a stress may exist inside the GaN film, and various kinds of dislocations may arise. As a result, the GaN film can have a dislocation density up to 109 to 1010 cm−2, seriously deteriorating the quality of the epitaxial film, and the defects usually act as non-radiative recombination centers, resulting in a decreased luminous efficiency. Thus, the key to the technology development of manufacturing the patterned sapphire substrate lies in the reduction of the defect density, to thereby substantially improve the quality of the epitaxial GaN film and increase the brightness. The growth direction of the dislocation of GaN may be changed by growing a GaN film on sidewall of the patterned substrate, such that the dislocations intersect with each other to form stacking fault due a 90° bend, thereby eliminating the defects. In addition, the three-dimensional stress can be released during the epitaxy to reduce the defect formation and the dislocation density inside the film to improve the epitaxial quality. Recent studies also found that the GaN film grown by the patterned sapphire substrate may have a reduced dislocation defect density of 108 to 109 cm−2, further enhancing the internal quantum efficiency and brightness of the light-emitting diode.
In the latest studies, a submicron-scale patterned substrate is also used to grow a light-emitting diode structure. For the patterned substrates with the same area, a reduced pattern size and an increased pattern number will increase the effective area of the lateral growth, thereby improving the lateral growth mechanism. This allows an easier way to change the growth direction and the formation of stacking fault, to eliminate the dislocation defect and significantly reduce the dislocation density inside the film. Also, because of the shorter spacing of the pattern, voids are easily formed during the epitaxy of GaN to block the propagation of defects, thereby improving the quality of the GaN epitaxial film. The studies indicate that a GaN film grown by the micron-scale patterned sapphire substrate may has a decreased dislocation density of 108 cm−2, and when the patterned substrate is in a submicron-scale, due to the increased level of stress released per unit volume, the dislocation density may be decreased to 107 cm−2 or less.
In the prior art, Taiwan Patent No. I396297 discloses a light emitting diode (LED), comprising a substrate having a micro-meter photonic crystal structure formed therein; a nano-scale photonic crystal structure as a buffer layer formed on the micro-meter layer substrate; a first type epitaxy layer formed on the nano-scale photonic crystal structure; a light emitting layer formed on the first type epitaxy layer; a second type epitaxy layer formed on the light emitting layer; a first contact electrode formed on the first type epitaxy layer; and a second contact electrode formed on the second type epitaxy layer.
Also, Taiwan Patent Publication No. 201251113 discloses a manufacturing method of an LED substrate, an LED substrate and a white light LED structure. The main object is to make an LED emit a high luminance white light with good color rendering index. A plurality of protrusions formed on the reflector of substrate have curved surface on their tops, and the protrusions have a bottom width of 2-4 μm, a height of 1.2-1.8 μm, and a spacing between the two adjacent protrusions may be 0.6-3 μm. The plurality of protrusions makes the InGaN epitaxy layer generate an ultraviolet with a 380-410 nm wavelength after electrify. The ultraviolet reflected by the reflector of the substrate and the protrusions stimulate the fluorescent compounds formed by mixing zinc oxide and yttrium aluminum garnet (YAG) to generate complementary light of the ultraviolet. After the ultraviolet and its complementary light are blended, a high luminance white light with good color rendering index is emitted by a package, and the white light can be used in illumination.
However, in the above-mentioned LEDs, the luminous efficiency thereof is mainly improved by forming a nano-scale porous photonic crystal structure or a micron-scale protruding particles on the substrate individually, and there are still inherent limitations on reducing the dislocation density or improving the luminous efficiency by the aforementioned micron-scale or nano-sacle structural design.
In addition, Taiwan Patent Application No. 102111662 filed by the present Applicant discloses a substrate for an opto-electrical device, wherein at least one opto-electrical device is formed on an upper surface of the substrate, characterized in that the upper surface of the substrate has a plurality of micron-scale structures and a plurality of submicron-scale structures to form a roughened surface, wherein the size of the submicron-scale structures is smaller than that of the micron-scale structures. As such, the optical diffusion rate of the substrate and the quality of the epitaxial film material grown on a substrate can be improved, thereby enhancing the light extraction efficiency, and thus enhancing the overall light-emitting brightness of the opto-electrical device. This prior application further provides an opto-electrical device. This prior application filed by the present Applicant uses a combination of the micron-scale structure and the submicron-scale structure to enhance the quality of the epitaxial film or to improve the overall light-emitting brightness of the opto-electrical device.
Therefore, what is urgently needed in the art is to develop a patterned opto-electrical substrate and a light-emitting diode having the same, which can effectively reduce the dislocation defect density of a GaN film and increase the light-emitting efficiency of a light-emitting diode (LED), so as to improve the applicability and value of the light-emitting diode.